The present invention relates to a blind rivet and, more specifically, to a blind rivet able to keep the broken mandrel portion attached to the rivet from dropping off the rivet body after fastening.
A blind rivet comprises a rivet body consisting of a hollow sleeve and a hollow flange formed at one end of the sleeve with a larger diameter than the sleeve, and a mandrel consisting of a shaft portion extending from beyond the flange through the rivet body and a head integrally connected to the shaft portion with a diameter greater than the inner diameter of the sleeve arranged adjacent to the sleeve end on the side opposite that of the flange. During the blind rivet fastening operation, the shaft portion of the mandrel extending from the rivet body is inserted and held in the nose of the fastening tool. The rivet body with the mandrel passing through is inserted with the mandrel head in front into the attachment hole of the attached component aligned with the attachment hole of the attached member. When the mandrel head is sticking out of the rear surface of the attached member and the flange on the rivet body has come into contact with the attached component, the mandrel shaft extending from the flange on the attached component side is forcibly drawn out by the operation of the fastening tool until it breaks off. The forcible drawing of the mandrel shaft causes the mandrel head to pull the sleeve portion on the rear surface of the attached member towards the flange side. A portion of the sleeve (for example, the portion at the end near the mandrel head) expands outward radially and is deformed. The attached member and the attached component are interposed between the flange and the expanded and deformed portion of the sleeve, and the attached member and the attached component are fastened by the blind rivet. This fastening operation joins the attached component to the attached member.
Because the mandrel shaft portion of the broken mandrel held by the fastening tool is accommodated in the fastening tool in order to expand and deform the sleeve, this portion can be discarded from the fastening tool at a location away from the attached member at the end of the fastening operation. However, the broken shaft portion of the mandrel remains with the head on the rivet body connected to the attached member. Because the mandrel portion is not connected to the rivet body, gravity often causes it to drop off the rivet body. The mandrel shaft portion attached to the dropped off mandrel can contact the rear surface of the attached member, making noise and sometimes damaging the rear surface of the attached member. Therefore, the mandrel portion attached to the broken off rivet should be kept from dropping off the rivet body.
A particular blind rivet that attempts to overcome this problem is described in Patent Document 1, Japanese Published Unexamined Patent Application No. 6-147208 and in Patent Document 2, U.S. Pat. No. 2,756,624 and also in Patent Document 3, U.S. Pat. No. 5,102,274. In using this rivet, the broken off mandrel portion attached to the head has a head with a shape that keeps it from dropping off the rivet body. In the blind rivet of Patent Document 1 and Patent Document 2, the mandrel head has a shape with a nearly round horizontal cross-section in the root portion adjacent to the mandrel shaft and an oval-shaped horizontal cross-section in the tip portion. The end of the sleeve on the rivet body expanded and deformed by the mandrel head is first expanded and deformed into a round shape by the head portion which has a round horizontal cross-section. However, it is then deformed into an oval shape from the round shape by the expanded and deformed end of the sleeve, and finally into a shape in which the pair of long sides on the oval move closer to each other to cover the end surface of the rivet. The deformation causes the end surface of the broken mandrel head to be covered by the deformed portion of the end surface of the sleeve, and the mandrel portion attached to the broken rivet is kept from dropping off the rivet body.
The blind rivet in Patent Document 1 and Patent Document 2 can keep the broken mandrel portion attached to the rivet from dropping off the rivet body. However, when the head portion with a round horizontal cross-section in the blind rivet of Patent Document 1 and Patent Document 2 is deformed from a round horizontal cross-section to an oval-shaped horizontal cross-section by the sleeve which is expanded and deformed into a round shape by the head portion with a nearly round horizontal cross-section, the sleeve end of the rivet body is expanded and deformed again which weakens the strength of the expanded and deformed sleeve portion. As mentioned earlier, the attached member and the attached component are interposed between the flange and the expanded and deformed portion of the sleeve, and the attached member and the attached component are fastened by the blind rivet. This fastening operation joins the attached component to the attached member. When the strength of the expanded and deformed portion of the sleeve is weakened, the fastening strength of the blind rivet is reduced. As a result, the joining strength of the attached member and the attached component is also reduced.